What are the consequences in HashMap when a collision occurs if the key class does not implement equals and hashCode methods?

If the key class in HashMap does not override the equals() and hashCode() methods, the following problems may occur:

• By default, the equals() and hashCode() methods are inherited from Object, where hashCode is usually based on the memory address of the object, and equals compares references.
• This means that two different objects with the same logical values will have different hash codes and will not be considered equal.
• As a result, HashMap may store multiple keys that are logically equal as different entries.
• When trying to retrieve a value with a new object with the same data, the search will not find the corresponding key because hashCode and equals do not match.

Thus, the absence of a proper implementation of equals and hashCode leads to incorrect HashMap behavior: duplicate keys, inability to find values by logically equal keys, and performance degradation due to increased collisions.